Final answer:
The prominent tendencies used to define primates are their adaptations for climbing trees such as grasping hands and feet. Primates are warm-blooded and tend to have larger brains, stereoscopic vision, and flattened nails. Nocturnal habits, enhanced sense of smell, and cold-blooded metabolism are not primary primate characteristics.
Step-by-step explanation:
Among the options provided, the prominent tendencies used to define primates are grasping hands and feet. Primates have evolved from tree-dwellers, and this arboreal heritage has led to adaptations like rotating shoulder joints, widely separated big toes and thumbs that allow for gripping, and stereoscopic vision for depth perception. These adaptations for climbing trees, along with other characteristics such as larger brains, flattened nails, typically one offspring per pregnancy, and a trend toward holding the body upright, are what differentiate primates from other mammals. By contrast, nocturnal habits and enhanced sense of smell are less central to primate characteristics, as primates generally have a reduced reliance on smell and many are not strictly nocturnal. Primates are also not cold-blooded; they are warm-blooded animals that regulate their own body temperature.